Microtubule dynamics: Patronin, protector of the minus end

Suppression of Patronin deficiency by altered Hippo signaling in Drosophila organ development

The microtubule network is crucial for cell structure and function. Patronin is a conserved protein involved in protecting the minus end of microtubules. Conversely, Klp10A is a kinesin-like microtubule depolymerase. Here we report the role of Drosophila Patronin and Klp10A for cell survival in developing organs. Loss of Patronin reduces the size of organs by activation of a caspase in imaginal discs. Reduced wing by Patronin RNAi is suppressed by knockdown of Spastin (Spas) but not Katanin 60, suggesting that Patronin is inhibitory to the severing function of Spas at the minus end. Patronin RNAi phenotype is also recovered by overexpressing Death-associated inhibitor of apoptosis 1 (Diap1), a Yorkie target gene. Heterozygote mutations in Hippo pathway genes, including hippo and warts (wts), suppress the Patronin RNAi wing phenotypes. Furthermore, Patronin physically interacts with Merlin and Expanded while reducing their function. Patronin and Klp10A antagonistically regulate their levels. Wing phenotypes of Patronin RNAi are rescued by knockdown of Klp10A, consistent with their antagonistic interaction. Klp10A overexpression also causes organ size reduction that is partially suppressed by Diap1 overexpression or wts heterozygote mutation. Taken together, this study suggests that the antagonistic interaction between Patronin and Klp10A is required for controlling cell survival and organ size by modulating microtubule stability and Hippo components.

Context-dependent spindle pole focusing

The formation of a robust, bi-polar spindle apparatus, capable of accurate chromosome segregation, is a complex process requiring the co-ordinated nucleation, sorting, stabilization and organization of microtubules (MTs). Work over the last 25 years has identified protein complexes that act as functional modules to nucleate spindle MTs at distinct cellular sites such as centrosomes, kinetochores, chromatin and pre-existing MTs themselves. There is clear evidence that the extent to which these different MT nucleating pathways contribute to spindle mass both during mitosis and meiosis differs not only between organisms, but also in different cell types within an organism. This plasticity contributes the robustness of spindle formation; however, whether such plasticity is present in other aspects of spindle formation is less well understood. Here, we review the known roles of the protein complexes responsible for spindle pole focusing, investigating the evidence that these, too, act co-ordinately and differentially, depending on cellular context. We describe relationships between MT minus-end directed motors dynein and HSET/Ncd, depolymerases including katanin and MCAK, and direct minus-end binding proteins such as nuclear-mitotic apparatus protein, ASPM and Patronin/CAMSAP. We further explore the idea that the focused spindle pole acts as a non-membrane bound condensate and suggest that the metaphase spindle pole be treated as a transient organelle with context-dependent requirements for function.

Cell lines

We review the properties and uses of cell lines in Drosophila research, emphasizing the variety of lines, the large body of genomic and transcriptional data available for many of the lines, and the variety of ways the lines have been used to provide tools for and insights into the developmental, molecular, and cell biology of Drosophila and mammals.

A breach in the scaffold: the possible role of cytoskeleton dysfunction in the pathogenesis of major depression

Depression is one of the most common psychiatric disorders with inadequately understood disease mechanisms. It has long been considered that dendritic regression and decrease in the number of dendritic spines are involved in depression. Dendrites made up of microtubules and actin filaments form synapses with neighboring neurons, which come together as an important communication network. Cytoskeletal proteins undergo post-translational modifications to define their structure and function. In depression and other psychiatric disorders, post-translational modifications may be disrupted that can result in altered cytoskeletal functions. The disruption of microtubule and actin in terms of morphology and functions may be a leading cause of dendritic regression and decrease in dendritic spine in depression.